Mycelial compatibility groups in Sclerotium cepivorum

Abstract

Isolates of Sclerotium cepivorum from the Holland-Bradford Marsh, Ontario, Canada (n ¼ 146) and other locations (n ¼ 23) were evaluated for mycelial compatibility in agar culture and by transmitted light microscopy. In compatible interactions, hyphae of paired colonies anastomosed without cell deterioration or death at the point of fusion. In some incompatible interactions, hyphae of paired colonies were initially similar to those of compatible interactions but were later followed by deterioration or death of the fused cells. Incompatible interactions were associated with a red-brown colour that, in mass, produced a dark line at the junction of the two colonies. In other incompatible interactions, hyphae were observed to bypass or repel each other without fusing. Compatible and incompatible reactions were used to define nine mycelial compatibility groups (MCGs) among the isolates examined. Among isolates from Ontario, no incompatibility responses were observed among isolates from individual fields (e.g. no intrafield variability) but two MCGs were found among isolates from different fields (e.g. interfield variability). Among isolates from other regions, seven additional MCGs were detected that consisted of one to eight isolates. Two isolates were variable in reaction and were not assigned to any MCG. Three isolates from Switzerland were compatible with MCG-1 isolates from Ontario; and one isolate from Switzerland, two from England, two from New Zealand, and two from Australia were all intercompatible. The results establish that mycelial compatibility can be used to reflect genetic heterogeneity among isolates of S. cepivorum.

Genetic diversity in New Zealand populations ofSclerotium cepivorum

“…Similarly, as the fungus has no identified sexual stage that could allow genetic recombination, the presence of more than one MCG in a single field suggests multiple introductions into that field. The occurrence of multiple MCGs within fields in New Zealand is in contrast to the observations of Earnshaw & Boland (1997), who found only two MCGs and no intra-field variability in the HollandBradford Marsh, Ontario, Canada. However, Couch & Kohn (2000) subsequently found a third MCG in the Holland-Bradford Marsh, as well as a small amount of intra-field variability.…”

“…Mycelial compatibility was determined using the method of Earnshaw & Boland (1997). Inoculum plugs (diam.…”

“…Representative isolates from each of the MCGs found in New Zealand populations were paired against the reference strains. The results were used to name the New Zealand groups in accordance with those given by Earnshaw & Boland (1997). …”

“…In S. sclerotiorum, the formation of the incompatible reaction line between pairs of isolates (evidenced by a dark line or a strip of thin mycelium, and discontinuous sclerotia) is the consequence either of their failure to anastomose, or of cell death following anastomosis (Kohn et al 1990). Earnshaw & Boland (1997) established that mycelial compatibility could be used to reflect levels of genetic diversity in populations of S. cepivorum and demonstrated that compatible reactions between pairs of isolates of S. cepivorum were the result of successful anastomosis between strains. This anastomosis was subsequently confirmed with New Zealand strains by microscopic examination of the interaction zone between pairs of compatible isolates (Tyson & Fullerton unpubl.…”

“…The first objective was to determine the range and extent of MCGs amongst isolates of S. cepivorum taken from the major onion and garlic growing areas of New Zealand. Reference isolates from the collection of Dr G. Boland (University of Guelph, Canada) were used to correlate the MCGs found in New Zealand with those found in the previous study by Earnshaw & Boland (1997). The second objective was to use molecular techniques to examine the genetic variation within and between the MCGs.…”